Loop inductance compensator



Feb. 1, 1949. s. cUTLER l-:T AL

LOOP INDUCTANCE GOMPENSATOR Filed oct. so, 194s 24' MOLDED I6 Powosnsn /RoN m/W/ f m m MMM. M mn vJW. Y i M mw N Patented Feb. 1, 1949 naar Stanley Cutler and Calif., assignors Norton Wiener, LosAngeles, v tov Hoffman Radiov 'Corpora'- tion, a corporationof Calitorniav Appiioation ootobor 30, 194e, 'serial No. 106,663

This invention relates to radio equipment, particularly to loop antenna arrangementsfor use' transmitting with portable radio receiving or es upment.

Portable radio apparatus, and particularly portable radio receivers, are often provided with a loop-antenna which- Inaybey used in either of ttvo positions, namely folded within the cabinet, or, where increased pickup sensitivity is required, in 'a position extending 'outside the cabinet. Whensuch a loop is operated init's'fposition inside the cabinet-*ofthe apparatus, itis generally' in close proximity to the'receiver chassis or other metal parts, while ifthe .cabinet is of metal and is made oi insulating the door toA thel antenna material to increase the sensitivity when thefanthe metallic cabinet material aroundfthe door opening acts: asf-ashorted turn coupled: toA theV loop.` In either case, the antenna. suffers adecrease 'of inductance, and' the. antenna circuit is. detuned with a consequent loss off sensitivity and'sel'ectivity, as compared tennai's usedinternally,

with conditions when. the loopY isoperatedfin its outboard position. Y Y

- Itis van objectv of' the. present invention toovere come the variation` sultingf from its movement between the two positions described above, whereby regardless of the positionl oithe antenna, the circuits of the alpparatus: areoperate'datA optimum sensitivity and selectivity. A further object is to accomplishvthe' compensation for the changing relation of antennatoadjacent materials in a completely automatic manner, whereby the desiredicompensation is eflected without the necessity of any conscious action on the part oftheuser inr adjusting the antenna. means for achieving the aboveV results without complication of existing designs of cabinets or antennas, and in a very `simplefand economical manner.

Anf ancillary object oi theinvention is vto provide for the compensation.. indicated above in such a manner that minor adjustments of the degree of. compensation simply, to vtake care` of possible production variations in the relationships of antennas to the other parts of the apparatus.`

A still further object is to accomplish the above Vresults without adversely affecting the QT Aof the antenna to any appreciable extent. As pointed out below, under some circumstances the effective Q of the antenna may actually be increased over that of an uncompensated antenna.

The above and other objects and advantages of maybel accomplished Very 251A in antenna 'inductance re- Vever, such .an antenna is moved 4 Claims.v (C1. 250k-3&5@

the invention will best be understood by reference tothe following description orcertain specio embodiments of' ourr invention, takenA in connection with the accompanying' drawings, in which: Fig; I is a' side elevationaliview of a portablel radio receiver cabinet providedv with ourV invention; the' antenna being vin extended position,

Fig, 2 is alplan view off the same, Fig: 3 is a view similar'to Fig; 1v but with the antenna in its closed position, parts being shown in section, and

Fig. 4 is a' view similar to Figgz but showing a slightly modied form of antenna compensating slug. f

Referring' now to Fig. l of the drawings, there is shown a radio receiver cabinet lll of usual construction, provided with a hinged door I2 giving access to a loop antenna M'hingedly mounted on said door. The cabinet Ill may be of metal or of some insulating material, such as wood, but in either'event c th'edoori l2' will usually be of an insulating material pick-up when' the tion'. It'will be observed that when the antenna is in the full-line position of Fig. 1, it is spaced some'distance from the cabinet` lo, and hence operates essentially in freeY space. When howto its'closed Iposition'withinthe cabinet il), as indicated in Fig. 3,

` the metal partsof the'chassis I3, or to the metal inductance. of `the antenna is no A Vstill further Objectis to provide a l2, so that the longer properly matched to the tuned circuits of the equipment. In' order to overcome the above undesirable surrounding the opening of door `change in the properties of the antenna, we pro-A vide a slab i o' molded powdered iron, which is secured to the inside of door IZ vin such a manner'that it lies within the centralturn of the loop antenna Id whenever the'latter is in its folded position, as indicate'd'in dotted lines in Fig. 1 and in lull lines in Fig. This location of the slab ISL/leans that it has substantially no eflect upon the inductance of the loop when the latter is in the 'fuir une position of Fig. 1, but it operates to increase the in'ductance of the loop Whenever the latter is 'folded dovvnintoV the dotted line |position of Fig. 1, as it must be to be received within the cabinet I0.

When the door and the loop are folded into the cabinet il, occupying theA position shown in Fig. 3, the proximity of metal parts thereto tends to decrease the loop inductance due to the effects mentioned above. Now, however, the presence of F slab I6 within the loop increases its inductance in order to increase the signal Y antenna is in itsfclosed posias compared with the antenna in free space, and by proper selection of the permeability, shape, size and position of such slab, the increase in inductance due thereto can be made precisely equal to the decrease resulting from the antennas being folded into the cabinet.

We have found that a molded slab of low-loss powdered iron, approximately as@ to 1A; inch in;

thickness, and so located on door I2 as to lie in or very near and parallel to the plane of the folded loop, is satisfactory to perform the compensation required in average installations. It is preferred to make the slab somewhat smaller than the dimensions of the innermost turn of the loop, so that its position may be Varied somewhat in its own plane. Such an adjustment permits small production variations in antenna inductance to be taken care of, since a movement of the slab from an exactly centered position to a position closer to part of the inside loop turn will increase the degree of compensation eiected.

It is important that the iron slab be so located that none of the turns of the antenna cross the surface of the iron, since this Vwould increase the distributed capacitance of the loop, and the antennacircuit would not track or stayin resonance at the high frequencyend of the tuning band.

In the event that the inside turn of the loop it is of relatively large diameter, compensation may be eiected with` a minimum of inductive material by forming the` slab as a hollow ring shaped to t within the inside turn of the loop, with the core of the slab empty of material. This modification is illustrated in Fig. 4, wherein i8 designates a loop antenna having a large inside turn area, and designates the slab of powdered iron having a'hollow center portion.

Any convenient means maybe employed to secure the compensating slab in place on the door S2. In Figs. 2 and 4 I have shownthe slabs as having a pair of apertures adapted to receive screws 2li threaded into the door. material, and provided Withoversize washers 2t. permitting the slabs to be moved about somewhat for adjustment purposes, yet readily clamped down to secure the slabs in adjusted position. Numeral 23 in Fig. l represents an insulating bushing surrounding the screws plane of the slab in the plane of the folded loop. However, any equivalent means for mounting the antenna compensating slab may be utilized, so long as the above conditions as to relative positions are satised. Y

As compared with antenna compensation, it will be observed that our system is simpler and hence more economical to provide in production, since it involves the addition of only one major part which has no electrical connections with the antenna or the set chassis. At the same time, minor adjustments to take care of production variations, both in antennas and in plished. Furthermore, in its open position, the Q of the antenna according to our invention is unaffected by the presence of the compensating means, While in its closed position the change in Q can be made negligible, or may even beinprior art methods of loop iron slabs, are readily accom- 24 and adapted to maintain the Y 4 creased by the use of iron having high permeability and high Q It is obvious that many changes and modifications can be made in the details and arrangelents of our invention without departing from the spirit thereof; in particular, we wish to point out that it is not essential that Ythe compensating slug lie in the plane of the loop,although this is a convenient arrangement when the slug is smaller than the inside turn of the loop. It is, however, desirable to have the plane of the slug parallel and as close as possible to the plane of the loop, particularly when a large change of inductance must-be compensated. We intend to claim as our invention all these and other modications. of the invention which come Within the scope of the appended claims.

We claim:

l. In combination with a loop antenna of the type mounted for movement on a support between twoV operative positions in which its inductance is diiierent, compensating means comprising a slab of magnetic material secured to said support in such a position as to lie substantially within the turns of said loop antenna when the latter is in one of its operative positions.

2. The invention in accordance with claim 1, and means for adjusting the position of said slab with respect to saidsupport.

3. In radio equipmentof the type comprising a cabinet, circuit components in said cabinet, a hinged closure forsaid-cabinet, and a substantially planar loop antenna mounted on said closure for movement between positions parallel to said closure and perpendicular thereto, the improvement which comprises a member of relatively high magnetic permeability secured to said closure in position to enter the magnetic eld of said antenna when thelatter is moved to its position parallel to saidv closure, whereby to compen sate for variations of inductance of said antenna as `the latter is moved from its perpendicular positionl to its parallel position.

4. The invention in Vaccordance with claim 3, in-,which said antenna is hingedly connected to said Vclosurealong an axis relatively spaced from the axis of rotationof said closure with reference tosaid cabinet.

. Y STANLEY CUTLER.

NORTON WIENER.

. REFERENCES CITED The'following references are of record in the file of this patent: Y

A UNITED STATES PATENTS Number Name Date 2,043,624 Leib June 9, 1936 2,266,262 Polydoroi Dec.` 16, 1941 2,315,315 Cairnes Mar. 30,1943 2,318,361 Bischoff May 4, 1943 2,335,969 Schaper Dec. 7, 1943 FOREIGN PATENTS Number Country Date 220,352 Great Britain Aug. 18, 1924 

